TP53 and neuroendocrine tumor of the appendix, well differentiated, low or intermediate grade: In appendiceal tumors, TP53 mutations rarely occur in low-grade appendiceal mucinous neoplasms [23], in which they are a marker of progression to high-grade tumors, and high-grade appendiceal mucinous neoplasms [23,33], and with higher frequency in appendiceal adenocarcinomas, mucinous adenocarcinomas of the appendix [16,23,33], signet ring cell adenocarcinoma [33], and appendiceal goblet cell adenocarcinoma [37], whose aggressive properties are due, to a reasonable extent, to TP53 inactivation by mutations [33], as well as in well-differentiated neuroendocrine tumors of the appendix [33].